1. Field of the Invention
The present invention refers generally to a voice conference apparatus and a method for realizing a voice conference, and especially to a distributed digital wireless voice conference system.
2. Description of the Related Art
Radio-based voice conference systems are utilized wherever it is not possible to communicate directly within a group of people due to a large distance, too high a noise level or other reasons. Several people are to be able to speak to one another via wireless-connected hearing and/or speaking sets, with everyone being able to hear all other participants at any time. I.e., there is a duplex voice link to every participant.
Thus, in a modern voice conference system a voice link that is quasi free from delay and full-duplex-capable amongst a large number of talk-listen units is to be established. Here it is important for economical reasons to keep the installation expenditure as low as possible. Furthermore, it is very important that the system is structured modularly and is flexible to be extended to a system of quasi any size. Apart from that, it must be possible that resources already present can be used further. On the customer side, this particularly refers to cabling as well as terminals already present. On the producer side, circuit concepts already present are to be used further. The circuit technology used is to be easy to realize at low cost. Nowadays, excellent voice quality is also expected of a modern voice conference system. Specifically, interference signals coupled into the transmission link and into a conference node must be very low. Finally, it is necessary in wireless systems to utilize the radio resources available as effectively as possible. The sum of these requirements calls for the refinement of the as yet existing concepts for voice conference systems.
According to the prior art, voice conference systems with base stations coupled in an analog manner or wireless DECT private branch exchanges are typically used today. In conference systems with base stations coupled in an analog manner the mobile units connected to a base station conference with one another. Several base stations are coupled in an analog manner. The circuit required here for the forming of a conference includes analog circuit technology which with high expenditure is to prevent the coupling in of interferences into the analog signals used. This requires complex filters and is not feasible in an ideal manner. With a greater number of participants the interference noises would add up until the system became impracticable. Therefore, conference systems with base stations coupled in an analog manner do not meet the high demands placed on modern voice conference systems.
The installation expenditure is very high due to the necessary use of well-screened cables. Even with a low number of participants, the voice quality is not satisfactory, and interference effects may easily be coupled in. Also, flexible extension to a large number of participants is difficult due to the problems of the interference effects. Finally, today the use of analog circuit technology involves considerably higher cost compared to the use of digital circuits.
Apart from the conference systems with base stations coupled in an analog manner described above, wireless DECT private branch exchanges with digital voice transmission are customary today. Here the conference connection is made in a central unit. This also involves several disadvantages. Particularly the use of a central unit able to maintain a large number of radio links simultaneously is very costly. A modular extension of the system is very difficult to achieve. In addition, the use of a central unit involves spatial limitation of the conference system. Finally, the internal structure of a central unit differs greatly from that of a base station of a normal, i.e. not conference-capable, cordless telephone system. This leads to high costs.
The realization of a conference connection within a central unit is conventionally effected by the use of a signal processor adapted to perform the calculations required for the realization of a voice conference block. An example of such a signal processor is the SC14428 type by National Semiconductor. For further details regarding the capabilities of the signal processor, please refer to the accompanying documentation.